Convert ActionCable javascript to ES2015 modules with modern build environment

We've replaced the sprockets `//= require` directives with ES2015
imports. As a result, the ActionCable javascript can now be compiled
with rollup (like ActiveStorage already is).

- Rename action_cable/index.js.erb -> action_cable/index.js

- Add rake task to generate a javascript module of the ActionCable::INTERNAL ruby hash

  This will allow us to get rid of ERB from the actioncable javascript,
  since it is only used to interpolate ActionCable::INTERNAL.to_json.

- Import INTERNAL directly in ActionCable Connection module

  This is necessary to remove a load-order dependency conflict in the
  rollup-compiled build. Using ActionCable.INTERNAL would result in a
  runtime error:
  ```
  TypeError: Cannot read property 'INTERNAL' of undefined
  ```
  because ActionCable.INTERNAL is not set before the Connection module
  is executed.

  All other ActionCable.* references are executed inside of the body of a
  function, so there is no load-order dependency there.

- Add eslint and eslint-plugin-import devDependencies to actioncable

  These will be used to add a linting setup to actioncable like the one
  in activestorage.

- Add .eslintrc to actioncable

  This lint configuration was copied from activestorage

- Add lint script to actioncable

  This is the same as the lint script in activestorage

- Add babel-core, babel-plugin-external-helpers, and babel-preset-env devDependencies to actioncable

  These will be used to add ES2015 transpilation support to actioncable
  like we have in activestorage.

- Add .babelrc to actioncable

  This configuration was copied from activestorage

- Enable loose mode in ActionCable's babel config

  This generates a smaller bundle when compiled

- Add rollup devDependencies to actioncable

  These will be used to add a modern build pipeline to actioncable like
  the one in activestorage.

- Add rollup config to actioncable

  This is essentially the same as the rollup config from activestorage

- Add prebuild and build scripts to actioncable package

  These scripts were copied from activestorage

- Invoke code generation task as part of actioncable's prebuild script

  This will guarantee that the action_cable/internal.js module is
  available at build time (which is important, because two other modules
  now depend on it).

- Update actioncable package to reference the rollup-compiled files

  Now that we have a fully functional rollup pipeline in actioncable, we
  can use the compiled output in our npm package.

- Remove build section from ActionCable blade config

  Now that rollup is responsible for building ActionCable, we can remove
  that responsibility from Blade.

- Remove assets:compile and assets:verify tasks from ActionCable

  Now that we've added a compiled ActionCable bundle to version control,
  we don't need to compile and verify it at publish-time.

  (We're following the pattern set in ActiveStorage.)

- Include compiled ActionCable javascript bundle in published gem

  This is necessary to maintain support for depending on the ActionCable
  javascript through the Sprockets asset pipeline.

- Add compiled ActionCable bundle to version control

  This mirrors what we do in ActiveStorage, and allows ActionCable to
  continue to be consumed via the sprockets-based asset pipeline when
  using a git source instead of a published version of the gem.

1 files changed, 123 insertions, 125 deletions

diff --git a/actioncable/app/javascript/action_cable/connection.js b/actioncable/app/javascript/action_cable/connection.js
index 540f597303..4ad436f2c0 100644
--- a/actioncable/app/javascript/action_cable/connection.js
+++ b/actioncable/app/javascript/action_cable/connection.js
@@ -1,158 +1,156 @@
-//= require ./connection_monitor
+import ActionCable from "./index"
+import INTERNAL from "./internal"
 
 // Encapsulate the cable connection held by the consumer. This is an internal class not intended for direct user manipulation.
 
-const {message_types, protocols} = ActionCable.INTERNAL
+const {message_types, protocols} = INTERNAL
 const supportedProtocols = protocols.slice(0, protocols.length - 1)
 
-ActionCable.Connection = (function() {
-  const indexOf = [].indexOf
+const indexOf = [].indexOf
 
-  class Connection {
-    constructor(consumer) {
-      this.open = this.open.bind(this)
-      this.consumer = consumer
-      this.subscriptions = this.consumer.subscriptions
-      this.monitor = new ActionCable.ConnectionMonitor(this)
-      this.disconnected = true
-    }
+class Connection {
+  constructor(consumer) {
+    this.open = this.open.bind(this)
+    this.consumer = consumer
+    this.subscriptions = this.consumer.subscriptions
+    this.monitor = new ActionCable.ConnectionMonitor(this)
+    this.disconnected = true
+  }
 
-    send(data) {
-      if (this.isOpen()) {
-        this.webSocket.send(JSON.stringify(data))
-        return true
-      } else {
-        return false
-      }
+  send(data) {
+    if (this.isOpen()) {
+      this.webSocket.send(JSON.stringify(data))
+      return true
+    } else {
+      return false
     }
+  }
 
-    open() {
-      if (this.isActive()) {
-        ActionCable.log(`Attempted to open WebSocket, but existing socket is ${this.getState()}`)
-        return false
-      } else {
-        ActionCable.log(`Opening WebSocket, current state is ${this.getState()}, subprotocols: ${protocols}`)
-        if (this.webSocket) { this.uninstallEventHandlers() }
-        this.webSocket = new ActionCable.WebSocket(this.consumer.url, protocols)
-        this.installEventHandlers()
-        this.monitor.start()
-        return true
-      }
+  open() {
+    if (this.isActive()) {
+      ActionCable.log(`Attempted to open WebSocket, but existing socket is ${this.getState()}`)
+      return false
+    } else {
+      ActionCable.log(`Opening WebSocket, current state is ${this.getState()}, subprotocols: ${protocols}`)
+      if (this.webSocket) { this.uninstallEventHandlers() }
+      this.webSocket = new ActionCable.WebSocket(this.consumer.url, protocols)
+      this.installEventHandlers()
+      this.monitor.start()
+      return true
     }
+  }
 
-    close({allowReconnect} = {allowReconnect: true}) {
-      if (!allowReconnect) { this.monitor.stop() }
-      if (this.isActive()) { return (this.webSocket ? this.webSocket.close() : undefined) }
-    }
+  close({allowReconnect} = {allowReconnect: true}) {
+    if (!allowReconnect) { this.monitor.stop() }
+    if (this.isActive()) { return (this.webSocket ? this.webSocket.close() : undefined) }
+  }
 
-    reopen() {
-      ActionCable.log(`Reopening WebSocket, current state is ${this.getState()}`)
-      if (this.isActive()) {
-        try {
-          return this.close()
-        } catch (error) {
-          ActionCable.log("Failed to reopen WebSocket", error)
-        }
-        finally {
-          ActionCable.log(`Reopening WebSocket in ${this.constructor.reopenDelay}ms`)
-          setTimeout(this.open, this.constructor.reopenDelay)
-        }
-      } else {
-        return this.open()
+  reopen() {
+    ActionCable.log(`Reopening WebSocket, current state is ${this.getState()}`)
+    if (this.isActive()) {
+      try {
+        return this.close()
+      } catch (error) {
+        ActionCable.log("Failed to reopen WebSocket", error)
       }
+      finally {
+        ActionCable.log(`Reopening WebSocket in ${this.constructor.reopenDelay}ms`)
+        setTimeout(this.open, this.constructor.reopenDelay)
+      }
+    } else {
+      return this.open()
     }
+  }
 
-    getProtocol() {
-      return (this.webSocket ? this.webSocket.protocol : undefined)
-    }
+  getProtocol() {
+    return (this.webSocket ? this.webSocket.protocol : undefined)
+  }
 
-    isOpen() {
-      return this.isState("open")
-    }
+  isOpen() {
+    return this.isState("open")
+  }
 
-    isActive() {
-      return this.isState("open", "connecting")
-    }
+  isActive() {
+    return this.isState("open", "connecting")
+  }
 
-    // Private
+  // Private
 
-    isProtocolSupported() {
-      return indexOf.call(supportedProtocols, this.getProtocol()) >= 0
-    }
+  isProtocolSupported() {
+    return indexOf.call(supportedProtocols, this.getProtocol()) >= 0
+  }
 
-    isState(...states) {
-      return indexOf.call(states, this.getState()) >= 0
-    }
+  isState(...states) {
+    return indexOf.call(states, this.getState()) >= 0
+  }
 
-    getState() {
-      if (this.webSocket) {
-        for (let state in WebSocket) {
-          if (WebSocket[state] === this.webSocket.readyState) {
-            return state.toLowerCase()
-          }
+  getState() {
+    if (this.webSocket) {
+      for (let state in WebSocket) {
+        if (WebSocket[state] === this.webSocket.readyState) {
+          return state.toLowerCase()
         }
       }
-      return null
     }
+    return null
+  }
 
-    installEventHandlers() {
-      for (let eventName in this.events) {
-        const handler = this.events[eventName].bind(this)
-        this.webSocket[`on${eventName}`] = handler
-      }
+  installEventHandlers() {
+    for (let eventName in this.events) {
+      const handler = this.events[eventName].bind(this)
+      this.webSocket[`on${eventName}`] = handler
     }
+  }
 
-    uninstallEventHandlers() {
-      for (let eventName in this.events) {
-        this.webSocket[`on${eventName}`] = function() {}
-      }
+  uninstallEventHandlers() {
+    for (let eventName in this.events) {
+      this.webSocket[`on${eventName}`] = function() {}
     }
-
   }
 
-  Connection.reopenDelay = 500
-
-  Connection.prototype.events = {
-    message(event) {
-      if (!this.isProtocolSupported()) { return }
-      const {identifier, message, type} = JSON.parse(event.data)
-      switch (type) {
-        case message_types.welcome:
-          this.monitor.recordConnect()
-          return this.subscriptions.reload()
-        case message_types.ping:
-          return this.monitor.recordPing()
-        case message_types.confirmation:
-          return this.subscriptions.notify(identifier, "connected")
-        case message_types.rejection:
-          return this.subscriptions.reject(identifier)
-        default:
-          return this.subscriptions.notify(identifier, "received", message)
-      }
-    },
-
-    open() {
-      ActionCable.log(`WebSocket onopen event, using '${this.getProtocol()}' subprotocol`)
-      this.disconnected = false
-      if (!this.isProtocolSupported()) {
-        ActionCable.log("Protocol is unsupported. Stopping monitor and disconnecting.")
-        return this.close({allowReconnect: false})
-      }
-    },
-
-    close(event) {
-      ActionCable.log("WebSocket onclose event")
-      if (this.disconnected) { return }
-      this.disconnected = true
-      this.monitor.recordDisconnect()
-      return this.subscriptions.notifyAll("disconnected", {willAttemptReconnect: this.monitor.isRunning()})
-    },
-
-    error() {
-      ActionCable.log("WebSocket onerror event")
+}
+
+Connection.reopenDelay = 500
+
+Connection.prototype.events = {
+  message(event) {
+    if (!this.isProtocolSupported()) { return }
+    const {identifier, message, type} = JSON.parse(event.data)
+    switch (type) {
+      case message_types.welcome:
+        this.monitor.recordConnect()
+        return this.subscriptions.reload()
+      case message_types.ping:
+        return this.monitor.recordPing()
+      case message_types.confirmation:
+        return this.subscriptions.notify(identifier, "connected")
+      case message_types.rejection:
+        return this.subscriptions.reject(identifier)
+      default:
+        return this.subscriptions.notify(identifier, "received", message)
+    }
+  },
+
+  open() {
+    ActionCable.log(`WebSocket onopen event, using '${this.getProtocol()}' subprotocol`)
+    this.disconnected = false
+    if (!this.isProtocolSupported()) {
+      ActionCable.log("Protocol is unsupported. Stopping monitor and disconnecting.")
+      return this.close({allowReconnect: false})
     }
+  },
+
+  close(event) {
+    ActionCable.log("WebSocket onclose event")
+    if (this.disconnected) { return }
+    this.disconnected = true
+    this.monitor.recordDisconnect()
+    return this.subscriptions.notifyAll("disconnected", {willAttemptReconnect: this.monitor.isRunning()})
+  },
+
+  error() {
+    ActionCable.log("WebSocket onerror event")
   }
+}
 
-  return Connection
-
-})()
+export default Connection